I have enabled MSlogonV1 (Utra VNC 1.0.4 installed as a service) on several computers (around 300). I was able to connect on each computers.After few days and on some computers (not all) (windows 2008 server R2 and XP), it's not possible to connect anymore with this authentication scheme.

The only way is to restart the service.

See the mslogon.log during the issue :6/3/2013 14:03 Connection received from 127.0.0.1 using secretaccount account 6/3/2013 14:03 Connection received from 127.0.0.1 using secretaccount account 7/3/2013 10:41 Connection received from 127.0.0.1 using secretaccount account

Credentials are accepted (can be seen in the connection status window) but the server disconnect the connection (connection closed due to communication error)